Arctic sea ice is melting at a significantly faster rate than projected by any of the 18 computer models used by the Intergovernmental Panel on Climate Change (IPCC) in preparing its 2007 assessments, according to a new study by scientists at the National Center for Atmospheric Research (NCAR) and the University of Colorado’s National Snow and Ice Data Center (NSIDC).

The study, “Arctic Sea Ice Decline: Faster Than Forecast?” will appear Tuesday in the online edition of Geophysical Research Letters. It was led by Julienne Stroeve of the NSIDC and funded by the National Science Foundation, which is NCAR’s principal sponsor, and by NASA.

While the ice is disappearing faster than the computer models indicate, both observations and the models point in the same direction: the Arctic is losing ice at an increasingly rapid pace and the impact of greenhouse gases is growing.

—Marika Holland, NCAR

The authors compared model simulations of past climate with observations by satellites and other instruments. They found that, on average, the models simulated a loss in September ice cover of 2.5% per decade from 1953 to 2006. The fastest rate of September retreat in any individual model was 5.4% per decade. (September marks the yearly minimum of sea ice in the Arctic.)

However, newly available data sets, blending early aircraft and ship reports with more recent satellite measurements that are considered more reliable than the earlier records, show that the September ice actually declined at a rate of about 7.8% per decade during the 1953-2006 period.

This suggests that current model projections may in fact provide a conservative estimate of future Arctic change, and that the summer Arctic sea ice may disappear considerably earlier than IPCC projections," says Stroeve.

—Julienne Stroeve

The study indicates that, because of the disparity between the computer models and actual observations, the shrinking of summertime ice is about 30 years ahead of the climate model projections. As a result, the Arctic could be seasonally free of sea ice earlier than the IPCC-projected timeframe of any time from 2050 to well beyond 2100.

The authors speculate that the computer models may fail to capture the full impact of increased carbon dioxide and other greenhouse gases in the atmosphere. Whereas the models indicate that about half of the ice loss from 1979 to 2006 was due to increased greenhouse gases, and the other half due to natural variations in the climate system, the new study indicates that greenhouse gases may be playing a significantly greater role.

There are a number of factors that may lead to the low rates of simulated sea ice loss. Several models overestimate the thickness of the present-day sea ice and the models may also fail to fully capture changes in atmospheric and oceanic circulation that transport heat to polar regions.

Although the loss of ice for March is far less dramatic than the September loss, the models underestimate it by a wide margin as well. The study concludes that the actual rate of sea ice loss in March, which averaged about 1.8% per decade in the 1953-2006 period, was three times larger than the mean from the computer models. March is typically the month when Arctic sea ice is at its most extensive.

The Arctic is especially sensitive to climate change partly because regions of sea ice, which reflect sunlight back into space and provide a cooling impact, are disappearing. In contrast, darker areas of open water, which are expanding, absorb sunlight and increase temperatures. This feedback loop has played a role in the increasingly rapid loss of ice in recent years, which accelerated to 9.1% per decade from 1979 to 2006 according to satellite observations.

Walt Meier, Ted Scambos, and Mark Serreze, all at NSIDC, also co-authored the study.

Modeling of complex nonlinear systems is very tricky. Ideally we would have many Earth like planets to observe under slightly different conditions to see how each responded. Unfortunately, we have but this one.

We do, however, understand the causal relationship between greenhouse gases and warming. There are potentially some negative feedback processes that might kick in and mitigate the effects. However, there are some positive feedback mechanisms that might kick in and result in really quick, really bad things happening. Science will never be able to prove which will happen. The only proof will be in hind sight.

A doctor talking to a patient that smokes 4 packs a day, can't in all honesty say that the patient isn't going to be that one rare smoker that lives to 97 and dies in a scuba diving accident. He can, however, tell the patient that from every shred of scientific evidence he is doing something that is very foolish and is highly likely to cause major health problems. We don't know everything about GHG and climate just like we don't know everything about smoking and health... but I think the wise course of action is perfectly clear in both cases.

Of all the pages on the web these these pages ought to have the most sane observers who fully understand that the electrification of ground transport is world altering; it's coming, and coming much faster than most think.

Within a decade it is possible that ground transport fossil fuel burning could decline by 60-80%. And not due to the hypocritical exhortations by knot-head politicians, but by the sheer economic attractiveness of paying the electrical equivalent of $0.25 per gallon equivalent of gasoline/diesel. Most of the worlds oil that is burned is done for ground transport.

Soon thereafter the global addition of carbon to the atmosphere by mankind will drop just as precipitously.

If you truly believe that its all mankind's fault, then shortly thereafter atmospheric CO2 will get eaten out of the atmosphere, by the Plants and the Oceans, and CO2 levels will settlee back toward pre-industrial levels.

If, as the new and latest scientific research is showing, it is the cyclical rise in Solar Radiance that is responsible for most of the warming we are seeing, on all the planets, that too is cyclical and is expected to decline in the second decade of the 21st century.

It has always been true that elevated CO2 levels are a result of warming and not a cause, occurring after the onset of warming as the oceans evaporate their absorbed CO2, like the fizz evaporating from a glass of opened Coca Cola left on a table. Gore was never able to get around that "inconvenient truth". Even those madcap scientists of the IPCC now agree.

Therefor Global Cooling is coming or more precisely will accelerate since the peak Earth temperature seemed to occur about 1998 and has declined since then by a very slight amount.It will happen long before 2050.

Frankly, it's best to meet Stan's skepticism with facts rather than derisive remarks. It certainly worked with me. He also thinks that CO2 emissions will go down anyway when we convert to PHEVs. Basically, he's approaching the problem from a different route--energy security.

It's not really worth the time or effort to convince him. He'll have to review the science for himself. That's what I did.

Arctic ice is nothing like glaciers of Greenland or Antarctica. It is mostly generated off north shore of Russia, and drifts over the pole to melt when it enters North Atlantic. Most of the ice is one year old, some – 2 years old, and multy-year ice is very small fraction. It is generated during winter with -40C temperature and no sun whatsoever for half a year, so it will not disappear completely under any circumstances. Warmer climate will lead to earlier end of ice cover south of Arctic Circle at best. Computer modeling of CO2 induced AGW over Arctic ice cover is junk, because main factors of spring and autumn ice extend and ice thickness are prevailing wind and ocean currents, which force ice into warmer waters, compact over the shore, etc.

Stan:

Arctic ocean was free of ice only gazillion years ago, when Greenland was part of Europe, continents were in different places than today, and most important of all – the Arctic Ocean was not in polar region – Earth rotated around different poles as it is today. Polar regions always have some ice.

Here's a fact for Stan. Last night I did a projection of atmospheric CO2 levels using the readings taken at the Mauna Loa Observatory in Hawaii. We are at 385 ppm of CO2 today and are on track to hit 400 ppm in May of 2013.

Critics can no longer deny that our planet is getting warmer, so now they are delaying any urgent action by telling themselves (and anyone else that will listen) that this is all part of a natural cycle.

The mean temperature of the earth is somewhere between 5C and 19C, depending on the set of data chosen. The most striking thing in common with all of these measurements is that the mean temperature of the earth is greater than 0C, i.e., greater than the freezing point of water.

So, if the temperature distribution across the globe were uniform, but the mean temperature maintained, then the earth would not support the formation of ice. This does not require a warming of the planet. It simply requires that the temperature distribution be "flattened" somewhat. Therefore, measuring the temperature of the planet by the quantity of ice extant is useless.

I have a fish tank at home. Its a pretty closed system. Inside there are guppies. There is also a filter and a number of plants. When the guppies and plants are in balance the guppies make Nitrogen compounds which the plants consume along with some beneficial bacteria on the rotating bio-wheel.

Guppies, being prolific, made lots of baby fish ... these fish radically raised the nitrogen levels in the tank. Doing so caused some of the fish to get sick and an algae bloom to appear in the tank.

You might ask why this analogy. We're producing the equivalent of a biological compound in vast quantities (CO2) and introducing it into our environment. No giant hand is going to come along and do a partial water change because we're cute pets.

I'm not saying that there is a causal relationship between the rise in atmospheric greenhouse gas concentrations and a corresponding decrease in the polar ice sheets. Honestly that wasn't my major in college. It would however be foolish not to think twice and work very hard to maintain the important balance which allows life to flourish on this planet. Make sure you've reviewed your sources and can bring them to the table before off handedly dismissing global warming as a real problem. I suspect there is merit to the research which has been done here.

Climate science has lousy track in prediction of future climate trends. For what it worth, here is last computer model prediction of NOAA (US National Oceanic and Atmosphere “Administration”) for the rest of 2007:

Note marked cooling predicted, especially in Pacific due to POSSIBLE switch of PDO (Pacific Decadal Oscillation) to “cool” phase, influencing weather patterns all around the globe. Compare with picture in article from Wiki about PDO:

http://en.wikipedia.org/wiki/Pacific_decadal_oscillation

Couple of days ago predictions of solar activity for incoming 24 and 25 cycles were released:

http://www.sec.noaa.gov/SolarCycle/SC24/index.html

Astrophysics are divided in prediction of cycle 24; if it will be according to low prediction, it WILL be cooling. Some scientists (like leading Russian astrophysics Habibullo Abdusamatov) predicts even smaller solar activity in cycle 25. If it will be the case, no amount of CO2 increase in atmosphere will prevent global climate from marked cooling.

Wow. What an unbelievable number of arrogant and ignorant posts disputing climate science findings. I guess the denialists feel really threatened by Green Car Congress. The site seems to be targeted by a cadre of crackpots. What a waste of protoplasm. My hat's off to those who can show patience to folks who would rather stroke their egos than help preserve the planet.

The sunspot cycle is 11 years and the PDO cycle is described in the Wikipedia article as running 20-30 years. Climatological data has indicated a gradual rise in temperature over 100 years. Are we talking about the same time scale?

You know, it's possible to be a proponent of alternative energy without buying into climate change. Energy security, the desire to not buy oil from places like Saudi Arabia and Venezuela, etc.. But the end result will be the same: less CO2 emissions due to increased efficiency and carbon-neutral biofuels.

The goals are the same. But if we get stuck on the whys instead of the hows, we'll never get anything done.

PDO is thought to be major factor influencing about 30 years global temperature oscillation, overlaid on general warming trend of 20 century. It explains why global temperature rose from 1910 to 1940, then dropped to 1970s, rose to around 1998, and is about unchanged since. For arctic region such oscillation is visible most:

Cervus, I agree about not getting stuck. Personal choice helps a lot and I have gone to transporting my children by bicycle. But a big necessary piece is gov. action re building codes, carbon tax, research, etc. To me the GW "sceptics" to use the most polite word, are little different from folks who for example oppose scientific medicine with claptrap about shark cartilage, etc. In a word insufferable.